1. Field of the Invention
The present invention relates to an airbag for a front passenger's seat that is mounted on a top area of an instrument panel of vehicle in front of a front passenger's seat.
2. Description of Related Art
As known in JP 2006-103654, for example, a conventional airbag for a front passenger's seat is stored in a housing on a top area of the instrument panel or dashboard. In operation, fed with inflation gas, the airbag deploys upward and rearward in such a manner as to fill a space between the top plane of the dashboard and a windshield. The airbag is configured to inflate into a generally square conical shape whose front end is the top of the square cone and includes a round gas inlet port for introducing inflation gas in the vicinity of a lateral center of a front end of a lower side of the square cone at inflation. The airbag is attached to the housing at the periphery of the gas inlet port. Further, at full inflation, the airbag includes at a laterally central area at least in a rear region a recess that recesses forward and extends generally vertically, and a pair of raised regions that project rearward relative to the recess on the left and right of the recess and each extend vertically. The tops of the raised regions are formed by outer joints that join peripheral edges of left outer panel and right outer panel that constitute lateral portions of the airbag and corresponding peripheral edges of a pair of left inner panel and right inner panel that are located at an inner area in the lateral direction of the airbag. The leading end of the recess is formed by an inner joint that joins inner peripheral edges of the left and right inner panels together.
In the above airbag, the left inner panel and right inner panel each have a band shape sharply curved in a generally C-shape because those panels form an extensive area from top to rear bottom via rear side except the vicinity of the gas inlet port in the lateral center of the airbag at full inflation. The left outer panel and right outer panel are comprised of a single base cloth that extends from the periphery of the gas inlet port in a laterally symmetric contour approximating a butterfly configuration. These airbag panel configurations have been barriers to improving panel yield and therefore reducing manufacturing cost. Furthermore, upon airbag deployment, stress concentration occurs on an end of the leading end of the recess, i.e. the inner joint that joins the inner peripheral edges of the left and right inner panels together, because the end is located at the vicinity of the gas inlet port, i.e., at the vicinity of the front end of the fully inflated airbag. More specifically, in the initial stage of airbag deployment, a strong tension force acts on the periphery of the gas inlet port in the anteroposterior direction, i.e. in the direction the airbag deploys. Thereafter, when the airbag unfurls laterally, there arises another strong tension force acting in the lateral direction. Therefore, the strong tension forces work on the end of the inner joint located at the vicinity of the gas inlet port in four directions and thereby causing stress concentration. In order to cope with this problem, a separate reinforcing patch or the like has been needed to reinforce the end of the inner joint.